Electronic ballast systems for operating fluorescent lamps are well known and some are disclosed in U.S. Pat. Nos. 5,808,421, 6,031,342 as well as other patents. Electronic ballast systems typically convert a low frequency alternating current source having a relatively low frequency in the range from 50 to 60 Hz to a higher frequency typically in the range of 30–40 kHz. The conversion commonly involves a two stage process, wherein the ac oscillation having a frequency of 50 to 60 Hz is first rectified to a dc voltage and then this dc voltage is chopped at a higher frequency to produce alternating current in the frequency range of 30–40 kHz, which is used to excite the fluorescent lamp. The electronic ballast circuits advantageously perform the desired function for operating fluorescent lamps and reduce the energy consumption, compared to non-electronic ballast circuits, and especially compared to incandescent lamps. However, the conventional electronic ballast circuits typically employ a forced ignition for rapid start of the fluorescent lamps, but with this technique the voltage reaches as high as 2.000 volts. This unfortunately consumes and quickly destroys the cathodes of the fluorescent lamps. It is desired, however, that an electronic ballast circuit be provided that through a soft starting mode, energizing the lamp slowly, following a starting sequence controlled by an electronic chip, the voltage of the cathodes of the lamps only raises to 1.000 volts, and therefore it lengthens the operating life of the fluorescent lamps.
Electronic ballast circuits are typically selected to have parameters that operate for particular input frequency oscillation. For example, the electronic ballast circuit may have parameters selected so as to operate with the 110 volt, 60 Hz typically found in the United States, whereas other ballast circuits may have parameters selected to operate with 220 volts, 50 Hz typically found in European countries. It is desired to provide a ballast circuit that operates with the universal input covering the range from between 108 to 305 volts at a frequency range between 50–60 Hz.
Further, it is desired to provide an electronic ballast circuit that handles various types of fluorescent lamps such as, T2, T5, T8, T10, T12, 20W, 32W, 40W, 56W, 58W, 70W, linear, circular, 2D, twin tube, compact or U-shaped type fluorescent lamps.
Because fluorescent lamps have a lower energy consumption compared to incandescent lamps, they are extensively used in industrial and commercial environments, which commonly require emergency lighting. It is desired to provide for electronic ballast system for operating one or more fluorescent lamps and having a subsystem with a battery, along with a battery charger, and associated logic to provide for emergency lighting.
Electronic ballast systems that operate fluorescent lamps are commonly plagued by the disadvantage that they produce electromagnetic interference (EMI) and radio frequency interference (RFI). It is desired to provide for an electronic ballast system that reduces or even eliminates the EMI/RFI noise commonly produced by the electronic ballast systems.
Electronic ballast circuits commonly employ inductive loads, which act to lower the power factor, which, in turn, increases the consumption of current and, thereby, reduces the efficiency related to fluorescent lamps. It is desirable that an electronic ballast circuit be provided with a power factor correction circuit that allows for the creation of a power factor that approaches unity, thereby furthering the efficiency of the electronic ballast system.